POPULATION III STARS AROUND THE MILKY WAY
POPULATION III STARS AROUND THE MILKY WAY
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DOI：
10.3847/0004-637x/820/1/59
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发表时间：
2016-03
期刊：
影响因子：
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通讯作者：
Y. Komiya;T. Suda;M. Fujimoto
中科院分区：
文献类型：
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作者：
Y. Komiya;T. Suda;M. Fujimoto
我们探究了观测由原始气体形成的第三星族（Pop III）恒星的可能性。质量低于0.8个太阳质量（M⊙）的第三星族恒星理应存活至今，尽管目前尚未观测到，但银河系晕中存在低金属丰度（如[Fe/H]）的恒星，这表明第三星族恒星在诞生后，其表面受到了来自星际气体中吸积金属的污染。在本文中，我们研究了第三星族恒星从其所在的微型晕中逃逸的情况，考虑到当大质量的主星作为超新星爆发时，双星系统中的次星会被抛射出去。这些恒星因此避免了表面污染。通过基于扩展的普雷斯 - 谢赫特（Press–Schechter）合并树，结合层级结构形成来计算恒星形成和化学演化，我们证明了有数百到数万颗低质量的第三星族恒星从银河系的组成单元中逃逸。第二代及之后的极贫金属恒星也从微型晕中逃逸。我们通过评估暗物质晕的球形坍缩模型下合并树分支中微型晕之间的距离，来探讨这些逃逸恒星的空间分布。结果表明，逃逸恒星分布在恒星晕之外，其密度分布与暗物质晕相近，不过第三星族恒星在中心区域的聚集程度略高。6% - 30% 的逃逸恒星离开了银河系，进入星系际空间。基于这些结果，我们讨论了观测具有原始表面丰度的第三星族恒星的可行性。
We explore the possibility of observing Population III (Pop III) stars, born of primordial gas. Pop III stars with masses below 0.8 M⊙ should survive to date though are not yet observed, but the existence of stars with low metallicity as [ Fe / H ] in the Milky Way halo suggests the surface pollution of Pop III stars with accreted metals from the interstellar gas after birth. In this paper, we investigate the runaway of Pop III stars from their host mini-halos, considering the ejection of secondary members from binary systems when their massive primaries explode as supernovae. These stars save them from surface pollution. By computing the star formation and chemical evolution along with the hierarchical structure formation based on the extended Press–Schechter merger trees, we demonstrate that several hundreds to tens of thousands of low-mass Pop III stars escape from the building blocks of the Milky Way. The second and later generations of extremely metal-poor stars also escaped from the mini-halos. We discuss the spatial distributions of these escaped stars by evaluating the distances between the mini-halos in the branches of merger trees under the spherical collapse model of dark matter halos. It is demonstrated that the escaped stars distribute beyond the stellar halo with a density profile close to the dark matter halo, while Pop III stars are slightly more centrally concentrated. 6%–30% of the escaped stars leave the Milky Way and go out into the intergalactic space. Based on the results, we discuss the feasibility of observing the Pop III stars with the pristine surface abundance.